Two car-bomb blasts in the northern Lebanese city of Tripoli killed at least 42 people Friday, and the Lebanese Red Cross says more than 500 people were wounded.

One of the bombs exploded outside the Taqwa mosque as midday prayers were ending. That mosque is where Sheik Salem Rafei, a Salafi cleric opposed to Lebanon's militant Shi'ite Hezbollah group, usually prays. It was not clear whether he was inside.

The second car bomb went off about five minutes later outside the Al Salam mosque in Tripoli's Al Mina district.

Hassan Kamel was there:

"The sheikh was in the mosque praying and suddenly the explosion happened," he said.

Kamel said "destruction and bodies and wounded" were everywhere. "We condemn everything is happening here in Tripoli," he added.

There was no immediate claim of responsibility. The Shi'ite militia group Hezbollah quickly condemned the attacks, saying they appeared to be an attempt to incite even more sectarian violence ijn Lebanon.

Tensions have been on the rise during the civil war in neighboring Syria, especially in Tripoli, where Sunni Muslims who support the armed uprising in Syria have clashed repeatedly with Alawites who support President Bashar al-Assad.

The U.S. Embassy in Beirut condemned the bombings "in the strongest terms" and called all all parties to exercise calm and restraint.

Salman Shaikh, director of the Brookings Doha Center, warned via Twitter it is now only a matter of time before Sunni groups seek revenge, saying, "The cycle of sectarian tit-for-tat will only get worse."

An anti-Hezbollah Islamist group calling itself the Brigades of Aisha said it carried out a car bombing last week in Rweiss, a southern suburb of Beirut that is a Hezbollah stronghold. That blast killed 22 people and wounded more than 200.